Preparation and application of the hottest polymer

2022-08-23
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Preparation and application of polymer based nanocomposites (I)

polymer based nanocomposites refer to a new type of composite material formed by compounding other materials with nano size and polymer materials in various ways. In a broad sense, polymer based nanocomposites can be regarded as polymer based nanocomposites as long as at least one-dimensional size of a phase in its component is in the nano scale range

preparation methods and overview of several polymer based nanocomposites

I. intercalation composite method

intercalation composite method is an important method to prepare polymer based nanocomposites. Many inorganic compounds, such as silicate clay, phosphate, graphite, metal oxide, disulfide, etc., have typical layered structure as the main body, and organic polymers are inserted into the interlayer of the main body as the guest, so polymer based nanocomposites can be prepared. The intercalation composite method can be divided into three categories:

1) intercalation polymerization method

intercalation polymerization method is to disperse and insert the polymer monomer into the lamellar inorganic material (silicate, etc.) (generally, the monomer and lamellar inorganic material are dissolved in a solvent respectively), and then the monomer is polymerized in situ under additional conditions (such as oxidant, light, heat, etc.). The large amount of heat released during polymerization is used to overcome the Coulomb force between silicate sheets and make them peel off, so that the nano scale silicate sheets are combined with the polymer matrix in the form of chemical bonds. In 1987, Japan first used the intercalation method to prepare nylon 6/clay nanocomposites (NCH). The Institute of chemistry of the Chinese Academy of Sciences has studied the nylon 6/montmorillonite system and pioneered the "one-step" composite method, that is, cation exchange between montmorillonite layers, monomer insertion between layers and monomer polymerization are completed in one step

2) solution intercalation method

solution intercalation method is that the polymer chain is intercalated into the inorganic layer with the help of solvent in the solution, and then volatilizes to remove the solvent. This method requires a suitable solvent to dissolve the polymer and disperse the clay at the same time, and a large amount of solvent is not easy to recover, which is unfavorable to the environment. For example, polyethylene oxide, polytetrahydrofuran, polycaprolactone, etc. can be easily embedded into layered silicate and V2O5 gel in solution. Furuichi et al. Blended hydrophobic green earth (SAN) (quaternary amine salt exchange treatment) with toluene solution of polypropylene (PP) and heated to obtain pp/san nanocomposites. Ruiz hitzky et al. Mixed and stirred polyethylene oxide (PEO) with montmorillonite with different exchangeable cations to synthesize new polymer based nanocomposites with two-dimensional structure

3) solution intercalation method

solution intercalation method is to heat the polymer to the molten state and directly insert it into the interlayer under the action of static or shear force to prepare polymer based nanocomposites. For most important polymers, because there is no suitable monomer to intercalate or suitable solvent to dissolve the polymer and dispersion at the same time, the above two methods have their limitations, and the melt intercalation method can be easily realized. Experiments show that the composites obtained by solution intercalation, solution intercalation and intercalation polymerization have the same structure. Because melt intercalation is an innovative method first adopted by VAIA and giannelis of Cornell University in the United States. They prepared ps/clay and peo/clay polymer matrix nanocomposites by melt intercalation method

II. In situ compounding method

in situ compounding method is to melt and blend thermotropic liquid crystal polymers with thermoplastic resins, and process them by extrusion or injection molding. Because liquid crystal molecules are prone to spontaneous orientation, liquid crystal micro regions are oriented along the direction of external force to form a microfibril structure, which is fixed in situ when the melt cools, so it is called in-situ composite. Only when the micro area size of the material is less than 100nm can it belong to the category of nanocomposites. Li Xuedong, Guangzhou Institute of chemistry, Chinese Academy of Sciences, and others summarized in detail the fiber forming principle, rheological properties, mechanical properties, morphology distribution, crystallization behavior and factors affecting morphology and properties of in-situ fiber forming composites. The research and development of in-situ composites have made rapid progress. Lcp/pa alloy of ice company, lcp/pa12 of Hoechst Celanese company and lcp/pps alloy reinforced by 40% glass fiber have been commercialized. In situ polymerization is a new composite way that can make rigid molecular chains uniformly dispersed. In situ molecular composites are formed by dissolving rigid rod polymers in flexible polymers (or their monomers) and uniformly dispersing them in the polymer body. This method is called in situ polymerization. Qian Renyuan et al. Swelled and diffused the pyrrole monomer into the flexible chain polymer matrix, polymerized the pyrrole monomer in situ in the body with a certain initiator, and prepared in-situ composites with certain conductivity and improved the mechanical properties of the matrix material. Lindsey et al. Used micro crosslinked polyvinyl alcohol (PVA) as the matrix, constantly put forward higher, newer and more requirements to instruments and meters, polymerized pyrrole monomers in situ by electrochemical methods to form reinforced microfibrils, and obtained ppy/pva in-situ molecular composites. Zhang Shengmao and others synthesized tio2/poly (butyl propionate) nanocomposite films by in-situ polymerization. This nano coincidence film is expected to be used as a new special lubricating material under some working conditions. Jia Zhijie and others put the purified carbon nanotubes together with caprylamide and aminoacetic acid. It is suggested that domestic enterprises should pay close attention to the reactor mixing, and carry out polymerization under certain conditions to prepare nylon 6/carbon nanotube composites and blend pure commercial nylon 6 in a certain proportion. The results show that the nanocomposites have excellent properties

the author recently synthesized polystyrene TiO2 and polymethyl methacrylate/tio2 by in-situ polymerization. As lubricating oil additives, they have good anti-wear properties and can significantly improve the failure load of base oil

III. sol gel method

sol gel method uses alkoxy metal or metal salt and other precursors (water-soluble salt or oil-soluble alkoxide) to dissolve in water or organic solvent to form a homogeneous solution, the solute hydrolyzes to form nano particles and form sol, and the sol is transformed into gel after evaporation and drying. If the conditions are properly controlled, polymer matrix nanocomposites can be obtained without phase separation during the formation and drying of gel. In recent years, using the ingenious combination of sol-gel reaction and polymerization of metal alkoxides to prepare polymer matrix nanocomposites has become a new hotspot in material science. Sol gel method can be used in the following situations: (1) the precursor is dissolved in the pre formed polymer solution, and the precursor is hydrolyzed to form semi interpenetrating complex under the catalysis of acid, alkali or some salts; (2) The precursor and polymer monomers are dissolved in the solvent, and the hydrolysis and monomer polymerization are carried out at the same time. This method enables some completely insoluble polymers to be evenly inserted into the inorganic complex by in-situ formation. If the monomer is not crosslinked, it will form semi interpenetrating, and if the monomer is crosslinked, it will form complete interpenetrating; (3) In the above polymers or monomers, groups that can form chemical bonds with inorganic components can be introduced to increase the interaction between organic and inorganic components. This method has mild reaction conditions and uniform dispersion. Sun Rong and others synthesized oleic acid modified titanium dioxide nanoparticles with particle size of 40~60nm by sol-gel method. Niu Xinshu and others used tetrabutyl titanate and yttrium nitrate as raw materials as early as 1822 to prepare TiO2 nano materials doped with different amounts of Y by sol-gel method. Duhongwei et al. Used butyl titanate as precursor, N-methyl pyrrolidone (NMP) as solvent and glacial acetic acid as stabilizer to prepare TiQ2 sol by sol-gel method

the author has recently synthesized a series of surface modified TiO2 nanocomposites by sol-gel method. As a lubricant additive, it has good wear resistance and can significantly improve the failure compliance of the foundation

IV. direct dispersion method of nanoparticles

this method is to directly disperse nanoparticles in polymer matrix to prepare polymer based nanocomposites, in which polymer matrix is mostly functional materials with excellent performance. The advantage of this method is to obtain nanocomposites with high dispersion and small particles by controlling the conditions. The disadvantage is that particles are easy to agglomerate and difficult to disperse evenly. Usually, the surface of nanoparticles is covered with a layer of monolayer activator, which can prevent the agglomeration of nanoparticles themselves

v. LB film method

LB film method is to use the orientation properties of amphiphilic molecules with hydrophobic and hydrophilic ends at the gas-liquid interface to prepare high quality polymer based nanocomposites. At present, there are two main methods to prepare polymer matrix nanocomposites by LB film method: one is to use LB film containing metal ions, which is obtained by chemical reaction with H2S, etc; The other is that the prepared nanoparticles are directly assembled into LB films. Nanocomposites prepared by LB film method not only have the unique quantum size effect of nanoparticles, but also have the advantages of LB film molecular hierarchy, controllable film thickness, easy assembly and so on. If the type and preparation conditions of nanoparticles are changed, the photoelectric properties of the obtained materials can be changed. Thus, these materials have been widely used in the fields of microelectronics, optoelectronics, nonlinear optics and sensors

VI. microemulsion polymerization

gao, etc. in the microemulsion system of FeCl3 aqueous solution/toluene/methylpropionic acid, stir and reflux for 2h to obtain Fe2O3 coated with methylpropionic acid with particle size of 1.9~2.7nm, and then add an appropriate amount of crosslinking agent diethylbenzene and initiator azodiisobutyronitrile. The micro lotion was heated to 70 ° C and maintained for 7h, and then the polymer/fe2o3 gel was precipitated with methanol to prepare organic-inorganic composite membrane materials. Chengguoxiang et al. Determined the suitable conditions for water/span85-tween60/cyclohexane to reflect the micro lotion system, such as surfactant content, HLB value and water solubility value; then carried out acrylamide polymerization and AgCl, ZnS precipitation reaction in it, and prepared agcl/pam and zns/pam inorganic/organic nanocomposite particles with uniform size and regular shape, and the average particle size of about 20nm

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